Method of brightening bituminous street surfaces and bituminous street surfaces so brightened



Elite States Patent F 3,417,677 METHOD OF BRIGHTENING BITUMINOUS STREET SURFACES AND BITUMINOUS STREET SURFACES S0 BRIGHTENED Erwin Moser, Rheinfelden, and Johannes Schmitt, Efringen, Kirchen, Germany, assignors to Swiss Aluminum Ltd., Qhippis, Switzerland, a joint-stock company of Switzerland No Drawing. Filed Mar. 8, 1966, Ser. No. 532,572 Claims priority, application Switzerland, Mar. 10, 1965, 3,336/ 65 5 Claims. (Cl. 94-22) ABSTRACT OF THE DISCLOSURE Brightening of bituminous street coverings by scattering on the still hot and to some extent pasty covering layer aluminium granules having a diameter from 0.5 to mm. and having an especially intensely cleft and fissured surface, and rolling said granules into the covering layer.

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The present invention relates to a method of brightening bituminous street surfaces, and to bituminous street surfaces so brightened.

In rainy weather at night, the black surface of bituminous street coverings absorbs a good deal of the light of vehicles head lamps and many accidents result therefrom. In order to overcome this dangerous situation, it has been proposed to brighten the surface of such streets by means of aluminium powder or granules. Many setbacks however were experienced in this endeavour, mainly due to an insufficient adhesion of the aluminium particles to the street covering. The application of an aluminium powder of a determined granulation, the particles of which were bitumen coated met with a certain success, the aluminium layers having good adhesion and resisting even to rather heavy traffic. This latter method of street brightening however shows two distinct disadvantages: First, the previous bitumen coating of the aluminium particles raises the cost of the material. Secondly, the bright aluminium only appears when a considerable number of vehicle tires have passed and abraded the bituminous coating. Therefore, only the actual tracks where the vehicles have passed are brightened, whereas e.g. the border portions of the street do not show any brightening.

According to the present invention, these disadvantages of the bare as well as the bitumen coated aluminium particles are overcome, if spattered irregular granules are used. The expression spattered, irregular granules" means particles the surface of which is cleft and fissured in such a way, that the surface of the polyhedron obtained by connecting all the peaks and ridges of a particle by planes is 50% at the most, preferably 30% and less, of the actual surface of the particle. Flaky particles representing small lamellae are not spattered, irregular granules. Neither is this the case with the current aluminium granules, as their surfaces have no peaks and ridges worth mentioning. It is the same with atomized powder or with granules consisting of wire-formed particles.

In order to obtain spattered irregular granules according to the meaning of the expression explained above, the following method of production is used. From a receptacle containing molten aluminium or aluminium alloy and having at its bottom an outlet tube, there issues a free falling stream of molten metal of about 10 mm. diameter. Around the lower end of the outlet tube there is a circular nozzle (blast pipe) wherefrom a mixture of water and compressed air is blown from every side against the falling stream of molten metal at an angle of about 25.

3,417,677 Patented Dec. 24, 1968 The water drops hitting the molten metal particles are transformed to steam in the way of a little explosion, which gives birth to the clefts and fissures in the surface of the metal particle. The metal particles then fall into a water basin placed about 50 cm. below the lower end of the outlet tube, where they solidify. The amount of water being always the same, the air pressure may vary according to the size of the metal particles desired. High air pressure yields fine particles, low air pressure coarser ones.

For the purpose of street brightening, a particle size of 0.5 to 10 mm. largest diameter has been found suitable. The best results were obtained with diameters from 2 to 10 mm. When applied to the street surface, the metal particles have to be free from grease. These spattered, irregular granules are then applied to the bituminous street covering. The bituminous material has at this moment still to be of a certain viscosity, which means that it has to be hot. A temperature of 60 C. has been found to be just sufficient, but a range from to C. and more is preferred. Then the spattered, irregular granules are pressed into the still viscous, bituminous street covering by means of a cold road-roller. The bituminous material under the pressure of the roller penetrates into the clefts and fissures of the aluminium granules and thereby causes the metal granules and the bituminous material to be connected in such a way that it is practically impossible for the metal granules to be torn out from the street covering layer by the tires of a vehicle. Immediately after the application and rolling in of the metal granules, the brightening of the street surface is achieved over the entire width.

The spattered, irregular aluminium granules may obviously be blended with other bright material as e.g. quartz sand or bright stone granules. But in order to get good results, the essential portion of the brightening material has to consist of the spattered irregular aluminium granules.

The method of the present invention yields a good, bright street covering with good adhesion of the aluminium particles. Further improvement of the adhesion may be obtained by coating the spattered, irregular aluminium granules with a porous layer formed by chemical reaction from the base metal, e.g. by the Alodine process. In special cases, e.g. in a tunnel, it may be advantageous to incorporate in this porous layer a luminescent material, e.g. zinc sulfide. If the bituminous street surface in a tunnel is brightened by spattered, irregular aluminium granules incorporating luminescent material, a lesser lighting intensity than usual will be sufficient; or intermittent lighting up may be applied, as the car driver profits by the afterglow effect.

Instead of pure aluminium granules, granules from an aluminium alloy may be employed. In the case of streets with essentially heavy traffic, granules of greater hardness afford better resistivity to abrasion and may therefore be advantageous. An aluminium alloy with up to 25% silicium, up to 5% zinc, up to 4% iron and up to 1% magnesium may be useful for the purpose.

What is claimed is:

1. A method of brightening the surface of bituminous street covering, which comprises applying to a hot bituminous covering layer spattered, uncoated irregular granules of a metal of the class consisting of aluminium and aluminium alloys, the surfaces of these granules being free from grease and having essentially sharp peaks and ridges separated by deep clefts and fissures made by contacting water and the molten metal with each other to transform the water into steam which forms little explosions which result in the surfaces of the main portion of said granules being cleft and fissured in such a way that the polyhedron obtained by joining geometrically all the peaks and ridges of a granule by straight planes has a total surface area of not over 50% of the actual surface area of the granules, and pressing these granules into the surface to be brightened.

2. A method according to claim 1, wherein the largest diameter of the main portion of the spattered, irregular aluminium granules is from 2 to 10 mm., and wherein the clefts and fissures in the granules are formed by exposing the metal to water while in molten condition.

3. The method according to claim 2, wherein the largest diameter of the granules is from 2 to 10 mm, wherein said granules are free from bitumen, wherein said percentage is not over 30%, and wherein said granules are formed by spraying water on a falling stream of molten metal of not over said 10 mm. in thickness and solidifying the granules.

4. A street paving comprising a bituminous covering layer thereon, and spattered irregular uncoated granules of metal of the class consisting of aluminium and aluminium alloys embedded into the surface of the covering layer, the surfaces of these granules having essentially sharp peaks and ridges separated by deep clefts and fissures made by contacting water and the molten metal with each other to transform the water into steam which forms little explosions which result in the main portion of the granules having such character that the polyhedron obtained by geometrically joining all the peaks and ridges of a granule by straight planes has a total surface of at most 50% of the actual surface of the granules, and the main portion of the particles having a maximum diameter of from 2 to 10 mm.

5. A street paving as described in claim 4, wherein the main portion of said granules are formed by the action of water on the metal while hot, and have their largest diameter from 0.5 to 10 mm.

References Cited UNITED STATES PATENTS 1,986,591 1/1935 Meyer 941.5 2,036,373 4/1936 Taylor 94-1.5 2,260,461 10/1941 Kotts 94-1.5 2,379,741 7/1945 Palmquist 94-1.5 2,952,192 9/1960 Nagin 94--1.5 3,204,537 9/1965 Searight 94-1.5 3,291,011 12/1966 Defregger 941.5

JACOB L, NACKENOFF, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,417,677 December 24, 1968 Erwin Moser et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 61, "covering" should read coverings Column 3, lines 6 to 8, cancel "and wherein the clefts and fissu in the granules are formed by exposing the metal to water while in molten condition"; line 10, "The" should read A Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, J r.

Attesting Officer 

